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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 793 records · Page 44
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NASA NTRS2020

Simultaneous Retrieval of Surface Roughness Parameters for Bare Soils From Combined Active–Passive Microwave SMAP Observations

An active–passive microwave retrieval algorithm for simultaneous determination of soil surface roughness parameters [vertical root-mean-square (RMS) height ( s ) and horizontal correlation length ( l )] is presented for bare soils. The algorithm is based on active–passive microwave covariation, including the improved Integral Equation Method (I(exp 2) EM), and is tested with global soil moisture active passive (SMAP) observations. The estimated retrieval results for s and l are overall consistent with values in the literature, indicating the validity of the proposed algorithm. Sensitivity analyses showed that the developed roughness retrieval algorithm is independent of permittivity for E(sub s) > 10 [-]. Furthermore, the physical model basis of this approach (I(exp 2) EM) allows the application of different autocorrelation functions (ACF), such as Gaussian and exponential ACFs. Global roughness retrieval results confirm bare areas in deserts such as Sahara or Gobi. However, the type of ACF used within roughness parameter estimation is important. Retrieval results for the Gaussian ACF describe a rougher surface than retrieval results for the exponential ACF. No correlations were found between roughness results and the amount of precipitation or the soil texture, which could be due to the coarse spatial resolution of the SMAP data. The extension of this approach to vegetated soils is planned as an add-on study.

Correlation length↗
NASA NTRS1983

An ISEE 3 high time resolution study of interplanetary parameter correlations with magnetospheric activity

The coupling between the solar wind and the geomagnetic disturbances was examined using data from the ISEE-3 spacecraft at an earth-sun libration point and ground-based data. One minute data were used to avoid aliasing in determining the internal magnetospheric response to solar wind conditions. Attention was given to the cross-correlations between the geomagnetic index (AE), the total energy dissipation rate (UT), and the solar wind parameters, as well as the spatial and temporal scales on which the magnetosphere reacts to the solar wind conditions. It was considered necessary to characterize the physics of the solar wind-magnetosphere coupling in order to define the requirements for a spacecraft like the ISEE-3 that could be used as a real time monitoring system for predicting storms and substorms. The correlations among all but one parameter were lower during disturbance intervals; UT was highly correlated with all parameters during the disturbed times. An intrinsic 25-40 min delay was detected between interplanetary activity and magnetospheric response in quite times, diminishing to no more than 15 min during disturbed times.

Baker, D. N.↗
NASA NTRS2003

Parameters Describing Earth Observing Remote Sensing Systems

The Earth science community needs to generate consistent and standard definitions for spatial, spectral, radiometric, and geometric properties describing passive electro-optical Earth observing sensors and their products. The parameters used to describe sensors and to describe their products are often confused. In some cases, parameters for a sensor and for its products are identical; in other cases, these parameters vary widely. Sensor parameters are bound by the fundamental performance of a system, while product parameters describe what is available to the end user. Products are often resampled, edge sharpened, pan-sharpened, or compressed, and can differ drastically from the intrinsic data acquired by the sensor. Because detailed sensor performance information may not be readily available to an international science community, standardization of product parameters is of primary performance. Spatial product parameters described include Modulation Transfer Function (MTF), point spread function, line spread function, edge response, stray light, edge sharpening, aliasing, ringing, and compression effects. Spectral product parameters discussed include full width half maximum, ripple, slope edge, and out-of-band rejection. Radiometric product properties discussed include relative and absolute radiometry, noise equivalent spectral radiance, noise equivalent temperature diffenence, and signal-to-noise ratio. Geometric product properties discussed include geopositional accuracy expressed as CE90, LE90, and root mean square error. Correlated properties discussed include such parameters as band-to-band registration, which is both a spectral and a spatial property. In addition, the proliferation of staring and pushbroom sensor architectures requires new parameters to describe artifacts that are different from traditional cross-track system artifacts. A better understanding of how various system parameters affect product performance is also needed to better ascertain the utility of existing datasets and products as well as to specify the performance of new sensors and products. Examples of simulations performed for the Landsat Data Continuity Mission illustrate how various parameters affect system and product performance. Specific examples include the effects of ground sample distance, MTF, and band-to-band registration on various products.

Zanoni, Vicki↗
NASA NTRS2023

Phyllosilicate Decomposition on Bennu Due to Prolonged Surface Exposure

The Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer (OSIRIS-REx) mission to carbonaceous asteroid (101955) Bennu performed detailed mapping with a suite of instruments to characterize the composition and geology of its surface. Here we use data from the OSIRIS-REx Thermal Emission Spectrometer (OTES) instrument to investigate the relationship of OTES-derived spectral indices to other derived data products from OTES, the OSIRIS-REx Camera Suite (OCAMS), and the OSIRIS-REx Visible and InfraRed Spectrometer (OVIRS) at global and local scales. We quantitatively confirm that high values of the OTES silicate stretching slope (from ∼10 to ∼12 μm) in midday spectra that are indicative of thin and/or patchy dust cover are strongly associated with low thermal inertia (high porosity), low albedo boulders on Bennu. These high porosity boulders have brecciated textures with embedded clasts that likely originated on Bennu's parent body or during its disruption. The high porosity of these boulders is a key factor in the local production of the dust or its entrapment, as some large, brecciated boulders with a lower porosity have little evidence of dust. A second OTES spectral parameter, the silicate bending band depth near 22.7 μm applied to early evening spectra, is not correlated to thermal inertia, but is weakly to strongly correlated to albedo, OVIRS-derived 1.05 μm and 2.74 μm band depths, OVIRS-derived hydrogen abundance, and modeled nanophase troilite abundance. In several regions on Bennu there is a strong spatial relationship between these parameters, whereby areas with shallower silicate bending bands also have shallower 1.05 μm and 2.74 μm bands and lower albedo with higher nanophase troilite abundances. These correlations, combined with analysis of the silicate bending band in laboratory experiments of space weathered and mildly heated carbonaceous chondrites, suggests that decreased silicate bending band depths signify decomposition of phyllosilicates, likely Fe-bearing, due to space weathering or mild heating (<600 °C) via solar radiation during Bennu's time in near-Earth space. There is a strong association of larger silicate bending band depths in areas dominated by small rocks and unresolved material and in areas with small (≤ 25 m) craters identified as the spectrally reddest on Bennu, suggesting that this material has been more recently exposed due to impact and/or mass wasting processes. The shallowest silicate bending depths are associated with larger rocks and boulders that appear to have the longest surface exposure history, although there is band depth variation among them suggesting either initial composition variation that resulted in different responses to space weathering or heating, or varied exposure history of individual boulders themselves. We predict that any grains returned from Bennu with a significant surface exposure history will be characterized by shallower 22.7 μm, 1.05 μm and 2.7 μm band depths and increased sulfide (troilite) abundance, as well as textural and chemical evidence for phyllosilicate dehydration.

Asteroids, surfaces↗
NASA NTRS2010

High-Resolution Subtropical Summer Precipitation Derived from Dynamical Downscaling of the NCEP-DOE Reanalysis: How Much Small-Scale Information Is Added by a Regional Model?

This study assesses the regional-scale summer precipitation produced by the dynamical downscaling of analyzed large-scale fields. The main goal of this study is to investigate how much the regional model adds smaller scale precipitation information that the large-scale fields do not resolve. The modeling region for this study covers the southeastern United States (Florida, Georgia, Alabama, South Carolina, and North Carolina) where the summer climate is subtropical in nature, with a heavy influence of regional-scale convection. The coarse resolution (2.5deg latitude/longitude) large-scale atmospheric variables from the National Center for Environmental Prediction (NCEP)/DOE reanalysis (R2) are downscaled using the NCEP Environmental Climate Prediction Center regional spectral model (RSM) to produce precipitation at 20 km resolution for 16 summer seasons (19902005). The RSM produces realistic details in the regional summer precipitation at 20 km resolution. Compared to R2, the RSM-produced monthly precipitation shows better agreement with observations. There is a reduced wet bias and a more realistic spatial pattern of the precipitation climatology compared with the interpolated R2 values. The root mean square errors of the monthly R2 precipitation are reduced over 93 (1,697) of all the grid points in the five states (1,821). The temporal correlation also improves over 92 (1,675) of all grid points such that the domain-averaged correlation increases from 0.38 (R2) to 0.55 (RSM). The RSM accurately reproduces the first two observed eigenmodes, compared with the R2 product for which the second mode is not properly reproduced. The spatial patterns for wet versus dry summer years are also successfully simulated in RSM. For shorter time scales, the RSM resolves heavy rainfall events and their frequency better than R2. Correlation and categorical classification (above/near/below average) for the monthly frequency of heavy precipitation days is also significantly improved by the RSM.

NARR↗
NASA NTRS1972

Comparison of very-low-frequency auroral hiss with precipitating low-energy electrons by the use of simultaneous data from two Ogo 4 experiments.

Determination of the origin of auroral hiss by comparing the records of a vlf experiment (0.3 to 18 kHz) with simultaneous data obtained by an auroral-particle experiment having detectors for precipitating electrons at 0.7, 2.3, and 7.3 keV. It is found that, on the dayside of the earth, the occurrence of vlf hiss correlates well with precipitation events at 0.7 keV, but in general very poorly with activity in the higher-energy channels. Exact correlation between variations in vlf hiss intensity and in electron fluxes is rare even at 0.7 keV. In addition, vlf hiss tends to be observed over a somewhat larger spatial region than precipitating 0.7-keV electrons. It is concluded that, on the dayside, auroral hiss is generated by soft (E less than 1 keV) 'cusp region' electrons and that the lack of detailed correlation between the two phenomena is caused by propagation effects as the hiss travels downward and spreads from the generation region.

Hoffman, R. A.↗
NASA NTRS1993

Tropospheric gas composition and cloud structure of the Jovian North Equatorial Belt

Voyager IRIS observations of the NEB reveal longitudinal variability of 5-micron brightness temperatures of order 100 C. An anisotropic multiple scattering radiative transfer model is used to calculate synthetic spectra for comparison with the IRIS observations. Mie theory is used to model the spectral dependence of cloud extinction from 180 to 2300/cm. Cloud base locations within the model vary with assumed gas abundances according to thermochemical equilibrium. It is found that spatial variations in the abundance profiles of the condensible species, parahydrogen profiles and cloud optical depths can be used as tracers of the local and large-scale dynamics. The variation of cloud opacity is strongly correlated with the variation of relative humidity, which suggests that dynamic depletion of water vapor above the cloud forming level is the most plausible model to explain the spatial variation in the water profile within the NEB.

Carlson, Barbara E.↗
NASA NTRS1984

A new multifunction acousto-optic signal processor

An acousto-optic architecture for simultaneously obtaining time integration correlation and high-speed power spectrum analysis was constructed using commercially available TeO2 modulators and photodiode detector-arrays. The correlator section of the processor uses coherent interferometry to attain maximum bandwidth and dynamic range while achieving a time-bandwidth product of 1 million. Two correllator outputs are achieved in this system configuration. One is optically filtered and magnified 2 : 1 to decrease the spatial frequency to a level where a 25-MHz bandwidth may be sampled by a 62-mm array with elements on 25-micro centers. The other output is magnified by a factor of 10 such that the center 4 microseconds of information is available for estimation of time-difference-of-arrival to within 10 ns. The Bragg cell spectrum-analyzer section, which also has two outputs, resolves a 25-MHz instantaneous bandwidth to 25 kHz and can determine discrete-frequency reception time to within 15 microseconds. A microprocessor combines spectrum analysis information with that obtained from the correlator.

Berg, N. J.↗
NASA NTRS1971

Evaluation of acoustic testing techniques for spacecraft systems

External acoustic environments, structural responses, noise reductions, and the internal acoustic environments have been predicted for a typical shroud/spacecraft system during lift-off and various critical stages of flight. Spacecraft responses caused by energy transmission from the shroud via mechanical and acoustic paths have been compared and the importance of the mechanical path has been evaluated. Theoretical predictions have been compared extensively with available laboratory and in-flight measurements. Equivalent laboratory acoustic fields for simulation of shroud response during the various phases of flight have been derived and compared in detail. Techniques for varying the time-space correlations of laboratory acoustic fields have been examined, together with methods for varying the time and spatial distribution of acoustic amplitudes. Possible acoustic testing configurations for shroud/spacecraft systems have been suggested and trade-off considerations have been reviewed. The problem of simulating the acoustic environments versus simulating the structural responses has been considered and techniques for testing without the shroud installed have been discussed.

Cockburn, J. A.↗
NASA NTRS1978

Earth Radiation Budget Science, 1978

An earth radiation budget satellite system planned in order to understand climate on various temporal and spatial scales is considered. Topics discussed include: climate modeling, climate diagnostics, radiation modeling, radiation variability and correlation studies, cloudiness and the radiation budget, and radiation budget and related measurements in 1985 and beyond.

Source record↗
NASA NTRS1979

Spectral feature classification and spatial pattern recognition

This paper introduces a spatial pattern recognition processing concept involving the use of spectral feature classification technology and coherent optical correlation. The concept defines a hybrid image processing system incorporating both digital and optical technology. The hybrid instrument provides simplified pseudopattern images as functions of pixel classification from information embedded within a real-scene image. These pseudoimages become simplified inputs to an optical correlator for use in a subsequent pattern identification decision useful in executing landmark pointing, tracking, or navigating functions. Real-time classification is proposed as a research tool for exploring ways to enhance input signal-to-noise ratio as an aid in improving optical correlation. The approach can be explored with developing technology, including a current NASA Langley Research Center technology plan that involves a series of related Shuttle-borne experiments. A first-planned experiment, Feature Identification and Location Experiment (FILE), is undergoing final ground testing, and is scheduled for flight on the NASA Shuttle (STS2/flight OSTA-1) in 1980. FILE will evaluate a technique for autonomously classifying earth features into the four categories: bare land; water; vegetation; and clouds, snow, or ice.

Sivertson, W. E., Jr.↗
NASA NTRS1986

Investigation of the mode of compensation of Venus topography

The Venus gravity data derived from the Pioneer Venus Orbiter indicates a strong correlation of gravity to topography at all resolvable wavelengths. Focus was on an analysis in the spatial domain, using a geophysical model of topographic compensation together with the topography data to compute gravity vectors corresponding to the observed data and comparison of the calculated and observed gravity vectors.

Morgan, Paul↗
NASA NTRS1987

Optimizing a continuously variable filter in a hybrid optical correlator

In contrast to binary filters, continuously variable optical filters offer an ability to conpensate for certain imperfections in the optics of a hybrid correlator. Arbitrary static phase errors are introduced into a model of a phase-only filtering hybrid correlator, and a method of discovering a correction for them simulated. By a recursive technique a first approximation to the impulse's matched filter is adjusted (allowed to relax) so as to produce successively more localized distribution of the output in the correlation plane. The method is motivated by the development of continuously-variable phase-only spatial light modulators, but it is applicable to amplitude modulators and -with appropriate modification -- to binary modulators as well. The technique is robust against the form of the system's departure from ideal behavior.

Juday, Richard D.↗
NASA NTRS1988

Surface Contour Radar (SCR) contributions to FASINEX

The SCR was asked to participate in the Frontal Air-Sea Interaction Experiment (FASINEX) to provide directional wave spectra. The NASA P-3 carrying the SCR, the Radar Ocean Wave Spectrometer, and the Airborne Oceanographic Lidar was one of five aircrafts and two ocean research ships participating in this coordinated study of the air sea interaction in the vicinity of a sea surface temperature front near 28 deg N, 70 deg W. Analysis of data from the February 1986 experiment is still ongoing, but results already submitted for publication strengthen the hypothesis that off-nadir radar backscatter is closely correlated to wind stress. The SCR provided valuable information on the directional wave spectrum and its spatial variation.

Walsh, E. J.↗
NASA NTRS1988

Estimation of forest canopy characteristics and nitrogen cycling using imaging spectrometry

Canopy lignin concentration is strongly related to annual rates of nitrogen mineralization in a series of Wisconsin forest ecosystems. High spectral resolution Airborne Imaging Spectrometer (AIS) data were acquired over these forests to investigate the potential of remotely estimating canopy lignin content. Analysis of the data using a derivative transformation and correlative techniques suggests that lignin or a closely associated cellular constituent is influential in canopy reflectance. Spatial distributions of percent canopy lignin and annual rates of nitrogen mineralization for Blackhawk Island, WI, have been estimated from a mosaic of AIS imagery.

Wessman, Carol A.↗
NASA NTRS1993

Visual display aid for orbital maneuvering - Experimental evaluation

An interactive proximity operations planning system, which allows on-site planning of fuel-efficient, multiburn maneuvers in a potential multispacecraft environment, has been experimentally evaluated. An experiment has been carried out in which nonastronaut operators with brief initial training were required to plan a trajectory to retrieve an object accidentally separated from a dual-keel Space Station, for a variety of different orbital situations. The experiments have shown that these operators were able to plan workable trajectories, satisfying a number of operational constraints. Fuel use and planning time were strongly correlated, both with the angle at which the object was separated and with the existence of spatial constraints. Planning behavior was found to be strongly operator-dependent. This finding calls for the need for standardizing planning strategies through operator training or the use of semiautomated planning schemes.

Grunwald, Arthur J.↗
NASA NTRS1992

The form of spin orbitals for open-shell restricted Hartree-Fock reference functions

A new set of spin orbitals is proposed for single-reference correlation procedures based on an open-shell restricted Hartree-Fock (RHF) reference function. The spatial parts of the new spin orbitals are from an open-shell RHF calculation. These spin orbitals form a complete, orthonormal set. The RHF single determinant based on these spin orbitals is an S sub 2 eigenfunction, but a linear combination of S sub z eigenfunctions. The advantage of these spin orbitals is that equations for perturbation theory or coupled-cluster theory are symmetric in the spin indices and hence the number of independent parameters to be determined is dramatically reduced.

Jayatilaka, Dylan↗
NASA NTRS1993

ROSAT observations of the Chamaeleon star forming cloud

Two-soft X-ray images of the Chamaeleon I star forming cloud obtained with the ROSAT Position Sensitive Proportional Counter (PSPC) are presented. Seventy reliable, and perhaps 19 additional, X-ray sources are found. Up to Ninety percent of these sources are certainly or probably identified with T Tauri stars formed in the cloud. Twenty to 35 are probably previously unrecognized 'weak' T Tauri (WTT) stars. T Tauri X-ray luminosities range from log bar-L(sub x) less than 28.8 to 31.1 erg/s, or 10(exp 2) - 10(exp 4) times solar levels, with mean value of log bar-L(sub x) = 10(exp 29.2) erg/s in the 0.2-2.5 keV band. The X-ray luminosities of well-studied Chamaeleon cloud members are correlated with a complex of four stellar properties: effective temperature, mass, radius and bolometric luminosity. The spatial distribution, Hertzsprung-Russell (H-R) diagram locations of the stars indicate WTT and CTT are coeval. The total premain sequence population of the cloud is likely to be greater than 100 stars, with WTT stars outnumbering 'classical' T Tauri (CTT) stars by approximately 2:1.

Feigelson, E. D.↗